Multiscale static and fatigue analysis of the interface of explosion-welded aluminum-steel joints

This study investigates the static and fatigue behavior of explosion-welded aluminum-steel joints. Unlike previous studies, where fatigue cracks initiated in homogeneous weld toes or heat-affected zones, this work provides the first direct fatigue assessment of the explosion-bonded Al-steel interface. For this reason, using TriClad® bimetallic laminates, specimens were designed to locate the aluminum-steel interface at the middle of the gauge section, enabling targeted mechanical analysis. While explosion welding is well established, only limited studies have addressed the fatigue response of Al-steel transition joints. Most existing investigations consider assembled specimens or structural components, where failure typically initiates in the weld toe or root of cruciform joints, rather than at the explosion-bonded interface itself. In contrast, the present work employs specimens directly machined from explosively bonded bars, forcing rupture to occur at the interface and thus allowing a direct characterization of interfacial fatigue behavior. A comprehensive experimental approach was employed, combining monotonic tensile testing, fatigue analysis with infrared thermography, nanoindentation and Scanning Electron Microscopy (SEM). Results revealed a fatigue strength at 20 MPa (2 × 106 cycles), with cracks initiating predominantly at the interface. Thermographic analysis independently confirmed this threshold, while SEM revealed a stress-dependent shift from ductile to brittle fracture modes. The multiscale evaluation highlighted the need for interface-focused diagnostics in fatigue-critical structural applications, offering valuable insights for the deployment of bimetallic joints in shipbuilding and offshore engineering.